Browsing by Subject "Asphalt concrete"
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Item Constant displacement rate experiments and constitutive modeling of asphalt mixtures(Texas A&M University, 2006-04-12) Hariharakumar, PradeepThe focus of this dissertation is on constant displacment rate experiments on asphalt concrete and on developing continuum models in a general thermo-mechanical setting which will corroborate with the experimental results. Modeling asphalt concrete and predicting its response is of great importance to the pavement industry. More than 90 percent of the US Highways uses asphalt concrete as a pavement material. Asphalt concrete exhibits nonlinear response even at small strains and the response of asphalt concrete to different types of loading is quite different. The properties of asphalt concrete are highly influenced by the type and amount of the aggregates and the asphalt used. The internal structure of asphalt concrete keeps on evolving during the loading process. This is due to the influence of different kinds of activities at the microlevel and also due to the interaction with the environment. The properties of asphalt concrete depend on its internal structure. Hence we need to take the evolution of the internal structure in modeling the response of asphalt concrete. Experiments were carried out at different confinement pressures and displacement rates on cylindrical samples of asphalt concrete. Two different aggregates were used to make the sample -limestone and granite. The samples were tested at a constant displacement rate at a given confinement pressure. The force required to maintain this constant displacement rate is measured and recorded. The frame-work has been developed using the idea of multiple natural configurations that was introduced recently to study a variety of non-linear dissipative response of materials. By specifying the forms of the stored energy and rate of dissipation function of the material, specific models were developed using this frame work. In this work both a compressible and an incompressible model were developed by choosing appropriate forms of stored energy and rate of dissipation function. Finally the veracity of the models were tested by corroborating with the experimental results. It is anticipated that the present work will aid in the development of better constitutive equations which in turn will accurately model asphalt concrete in laboratory and in field.Item Controlling Thermal Properties of Asphalt Concrete and its Multifunctional Applications(2014-08-10) Shi, XijunControlling infrastructure temperature, especially flexible pavement, has attracted attention in both industrial and academic societies because: 1) material properties of asphalt, and corresponding structural responses and distresses are temperature dependent and 2) pavement surface temperature directly relates to various environmental or safety problems. This study investigates the feasibility of mitigating the temperature-related problems of civil infrastructures (especially asphalt pavement) by controlling thermal properties of the construction materials. To change thermal properties of asphalt concrete, expanded polypropylene (EPP) pellet and graphite were selected as the additives and mixed into asphalt concrete. Experimental tests are classified into two categories: 1) physical and thermal characterizations of raw materials including Scanning Electron Microscope and heat susceptibility tests, and 2) mechanical and thermal properties of the modified asphalt mixtures via indirect tensile test and hot disk test, respectively. The heat susceptibility test results show that use of EPP as an aggregate replacement is a better choice than the use of the melted-EPP as a binder modifier because it has a good heat susceptibility and is hard to melt at the HMA working temperature. The mechanical performances and thermal properties evaluation results show that by replacing the aggregate with EPP to have 18% by volume of total mixture, the indirect tensile strength was reduced by 17%, and the thermal conductivity and volumetric heat capacity decreased by 32% and 27%, respectively. By adding 4.8 vol. % of graphite, the indirect tensile strength decreased by 20%, and an increase of 43% in thermal conductivity was obtained. To simulate the effect of the thermally modified asphalt mixtures on the surface temperature of pavements and bridges, a series of heat transfer analysis were conducted using the finite difference heat transfer model. In addition, a case study of a building using EPP modified cement concrete was carried out to investigate the benefits of EPP modified concrete as a wall insulation. From the simulation results, it is concluded that adding graphite into asphalt mixture mitigates the urban heat island effect during summer by dropping the maximum surface temperatures of both pavement and bridge (3.1?C and 1.9?C, respectively, with 4.8% graphite), and the graphite modified asphalt concrete can reduce the use of deicing agents during winter by increasing the minimum surface temperature by 0.5?C for pavement and 0.2?C for bridge. On the other hand, adding EPP increases maximum surface temperature by 0.8?C for pavement and 1.0?C for bridge during winter, which show the potential for snow and ice removal application. In addition, the simulation shows that the EPP modified concrete can serve as a wall insulator.Item Two- and Three-Dimensional Microstructural Modeling of Asphalt Particulate Composite Materials using a Unified Viscoelastic-Viscoplastic-Viscodamage Constitutive Model(2013-08-13) You, TaesunThe main objective of this study is to develop and validate a framework for microstructural modeling of asphalt composite materials using a coupled thermo-viscoelastic, thermo-viscoplastic, and thermo-viscodamage constitutive model. In addition, the dissertation presents methods that can be used to capture and represent the two-dimensional (2D) and three-dimensional (3D) microstructure of asphalt concrete. The 2D representative volume elements (RVEs) of asphalt concrete were generated based on planar X-ray Computed Tomography (CT) images. The 2D RVE consists of three phases: aggregate, matrix, and interfacial transmission zone (ITZ). The 3D microstructures of stone matrix asphalt (SMA) and dense-graded asphalt (DGA) concrete were reconstructed from slices of 2D X-ray CT images; each image consists of the matrix and aggregate phases. The matrix and ITZ were considered thermo-viscoelastic, thermo-viscoplastic, and thermo-viscodamaged materials, while the aggregate is considered to be a linear, isotropic elastic material. The 2D RVEs were used to study the effects of variation in aggregate shape, distribution, volume fraction, ITZ strength, strain rate, and temperature on the degradation and micro-damage patterns in asphalt concrete. Moreover, the effects of loading rate, temperature, and loading type on the thermo-mechanical response of the 2D and 3D microstructures of asphalt concrete were investigated. Finally, the model parameters for Fine Aggregate Mixture (FAM) and full asphalt mixture were determined based on the analysis of repeated creep recovery tests and constant strain rate tests. These material parameters in the model were used to simulate the response of FAM and full asphalt mixture, and the results were compared with the responses of the corresponding experimental tests. The microstructural modeling presented in this dissertation provides the ability to link the microstructure properties with the macroscopic response. This modeling combines nonlinear constitutive model, finite element analysis, and the unique capabilities of X-ray CT in capturing the material microstructure. The modeling results can be used to provide guidelines for designing microstructures of asphalt concrete that can achieve the desired macroscopic behavior. Additionally, it can be helpful to perform 'virtual testing' of asphalt concrete, saving numerous resources used in conducting real experimental tests.Item Viscoelastic{Viscoplastic Damage Model for Asphalt Concrete(2010-10-12) Graham, Michael A.This thesis presents a continuum model for asphalt concrete incorporating non- linear viscoelasticity, viscoplasticity, mechanically-induced damage and moisture- induced damage. The Schapery single-integral viscoelastic model describes the nonlinear viscoelastic response. The viscoplastic model of Perzyna models the time- dependent permanent deformations, using a Drucker-Prager yield surface which is modified to depend on the third deviatoric stress invariant to include more complex dependence on state of stress. Mechanically-induced damage is modeled using continuum damage mechanics, using the same modified Drucker-Prager law to determine damage onset and growth. A novel moisture damage model is proposed, modeling moisture-induced damage using continuum damage mechanics; adhesive moisture- induced damage to the asphalt mastic-aggregate bond and moisture-induced cohesive damage to the asphalt mastic itself are treated separately. The analytical model is implemented numerically for three-dimensional and plane strain finite element analyses, and a series of simulations is presented to show the performance of the model and its implementation. Sensitivity studies are conducted for all model parameters and results due to various simulations corresponding to laboratory tests are presented. In addition to the continuum model, results are presented for a micromechanical model using the nonlinear-viscoelastic-viscoplastic-damage model for asphalt mastic and a linear elastic model for aggregates. Initial results are encouraging, showing the strength and stiffness of the mix as well as the failure mode varying with moisture loading. These initial results are provided as a an example of the model's robustness and suitability for modeling asphalt concrete at the mix scale.